Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jul 19, 2010 at 09:40:18AM +0200, Alexander Graf wrote:
> 
> On 19.07.2010, at 09:33, Gleb Natapov wrote:
> 
> > On Mon, Jul 19, 2010 at 08:28:02AM +0100, Richard W.M. Jones wrote:
> >> On Mon, Jul 19, 2010 at 09:23:56AM +0300, Gleb Natapov wrote:
> >>> That what I am warring about too. If we are adding device we have to be
> >>> sure such device can actually exist on real hw too otherwise we may have
> >>> problems later.
> >> 
> >> I don't understand why the constraints of real h/w have anything to do
> >> with this.  Can you explain?
> >> 
> > Each time we do something not architectural it cause us troubles later.
> > So constraints of real h/w is our constrains to.
> > 
> >>> Also 1 second on 100M file does not look like huge gain to me.
> >> 
> >> Every second counts.  We're trying to get libguestfs boot times down
> >> from 8-12 seconds to 4-5 seconds.  For many cases it's an interactive
> >> program.
> >> 
> > So what about making initrd smaller? I remember managing two
> > distribution in 64M flash in embedded project.
> 
> Having a huge initrd basically helps in reusing a lot of existing code. We do the same - in general the initrd is just a subset of the applications of the host OS. And if you start putting perl or the likes into it, it becomes big.
> 
Why not provide small disk/cdrom with all those utilities installed?

> I guess the best thing for now really is to try and see which code paths insb goes along. It should really be coalesced.
> 
It is coalesced to a certain extent (reenter guest every 1024 bytes,
read from userspace page at a time). You need to continue injecting
interrupt into a guest during long string operation and checking
exception condition on a page boundaries.

> Richard, what does kvm_stat tell you while loading the initrd? Are there a lot of PIO requests or are we simply looping inside qemu code?
> 
> 
> Alex

--
			Gleb.